We have recently found that peptides of viral surface glycoproteins can stimulate antivirus specific cytolytic thymus-dependent lymphocytes (CTL) in vitro. This has been accomplished for both Sendai and influenza viruses. This work is aimed at elucidating the chemical structures of stimulatory antigens from both viruses and at the mechanisms by which the stimulation occurs. The characterizations of the stimulator peptides will include the determination of the minimum peptides to induce antiviral antibodies. If funds permit, an attempt will be made to make molecular clones of the genetic information for these peptides in Escherichia coli so that the peptides can be obtained conveniently in large quantities from the bacteria.